The NSW education minister Adrian Piccoli has challenged the right of private schools to expel students, saying they are shirking their social responsibility for the sake of their reputations.

In an extraordinary attack in the wake of revelations that Trinity Grammar School expelled eight boys over a drug-related incident, Mr Piccoli said all taxpayer-funded schools had a moral obligation to help their students.

''Every school has a responsibility to address the behaviour of their students whether it is a $30,000 school or a government school,'' Mr Piccoli said.

''Just paying $30,000 doesn't give you the moral authority to say I don't want to deal with these kids … these are faith-based schools, and based on the faith I have, shifting the problem to another school is not the answer.''

The Sydney Morning Herald revealed this week that as many as eight year 8 students were asked to leave Trinity Grammar after an incident involving cannabis on the grounds of the inner-west school in November last year.

The school would not comment on any details of the incident, which was reported to police but no charges were laid, and it is not known to which schools the boys were moved.

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Mr Piccoli said no school should have to put up with ''bad behaviour, abusing teachers or drugs in schools'' but the community expected any school receiving public funding to ''manage students properly''.

''I don't have the power to tell independent schools what to do with their disciplinary processes,'' he said.

''But I think they do have an obligation to not simply find a student's behaviour unacceptable and just kick them out and allow it to become another school's problem.''

The head of the Association of Independent Schools NSW, Geoff Newcombe, said non-government schools were committed to ensuring the best outcomes for students who were expelled or asked to leave a school. ''Schools always make sure that students who leave have places to go and where help is needed, schools are often willing to bypass waiting lists to take a student from another school,'' Dr Newcombe said.

Dr Newcombe said there was a very supportive network within the independent sector.

Last year three 14-year-old boys in year 8 agreed to leave the exclusive Cranbrook School after a sexual incident involving a 14-year-old girl at "a gathering" in Sydney's eastern suburbs.

In 2011, Cranbrook also expelled four 14-year-old boys who were involved in buying and selling drugs.

Private schools do not have any requirement to report expulsion rates to the Department of Education but they do have to provide their policies to the Board of Studies, Teaching and Educational Standards.

Mr Piccoli said students were expelled from government schools but it was always the last resort and followed a period of suspension, counselling, extensive discussions with parents and placement in another school.

''Public schools can expel kids and they do but they can't just boot them out the door and let it become someone else's problem,'' Mr Piccoli said.